1. Field of the Invention
This invention relates to techniques for calibration of gun sights and, more particularly, to a laser precision bore sight assembly.
2. Prior Art
Previously, several different systems have been used for calibration of gun sights. To obtain an accurate alignment of a weapon bore sight or of a training device attached to a weapon, the first step in using a bore sight device is to rotate the bore sight device a minimum of 360 degrees to confirm that the alignment of the bore sight is concentric to the bore of the weapon. If the laser point that is projected from the bore sight device onto a target 10 meters away traces a circle on the target, then the axis of the bore sight device is not concentric with the bore of the weapon.
One type of alignment device, as disclosed in U.S. Pat. No. 4,825,258, uses a light source, such as a laser, which is coaxially mounted outside of the gun barrel on the outer end of a hollow cylindrical metal rod, the inner end of which extends into the bore of a gun barrel. The outer end of the hollow cylindrical rod is a larger cylinder which engages the inside wall of the gun barrel. The inner end of the hollow rod is smaller in diameter than the bore of the gun barrel and has an expandable, split end formed into a number of longitudinal metal fingers. The free ends of the longitudinal fingers are expanded outwardly using a cone-shaped mandrel which is drawn into the metal fingers with a screw which extends out through the hollow rod mechanism to force the cone-shaped mandrel into the fingers. In this manner, the ends of the metal fingers are pushed outwardly to engage the inner wall of the bore of the gun barrel. This arrangement is supposed to fix the inner end of the rod in position in the bore of the gun barrel and to maintain the axis of the rod in alignment with the axis of the bore of the gun barrel.
Note that, this type of a system can be rotated prior to the metal fingers engaging the walls of the gun barrel, but the fit of the fingers is too loose to maintain concentric alignment. If the metal fingers fully contact the barrel, the fingers catch upon the rifling grooves making it difficult to rotate the device while maintaining concentric alignment of a laser beam. When this arrangement is axially rotated in the gun barrel, some of the metal fingers engage the rifling grooves formed in the inside walls of the gun barrel while other metal fingers directly engage the walls of the gun barrel, which causes the inner end of a rotated rod to change its alignments in the gun barrel. The type of metal material used for the fingers also has an effect of the performance of such an arrangement. Use of a material, which is softer than the hard steel of a gun barrel, such as brass, results in wear of the metal fingers and uneven alignment of the metal fingers within the gun barrel so that the inner end of the rod does not remain coaxially aligned with the gun barrel. On the other hand, use of a harder material for the metal fingers results in wear and damage to the rifling within the gun barrel.
U.S. Pat. No. 5,365,669 discloses another system which uses a laser light source mounted in a cartridge-shaped housing that is contained in a cartridge chamber of a gun. This system is not adjustable and is subject to the axial offsets and misalignments between the axis of the cartridge chamber and the axis of the bore of the gun barrel.
What is needed is a system which maintains direct coaxial alignment of a laser light source along the axis of the bore of a gun barrel, particularly when that laser light source is axially rotated.